1. Field of the Invention
The invention relates to a clamping and/or spreading tool comprising a drive for displacement of a push or pull rod to which a movable jaw is fixed with respect to a support carrying a stationary jaw, in longitudinal direction of the push or pull rod.
2. Description of the Related Art
It is known to provide in particular clamping and/or spreading tools with a stepping gear transmission to cause stepwise approach of the movable jaw to the stationary jaw and, at the same time, apply the clamping forces required between the clamping jaws. Such a clamping and/or spreading tool is known from DE 39 17 473 which comprises a stepping gear transmission of which the step width per actuating stroke of a drive arm is sufficiently great and a relatively small actuating force can give rise to clamping forces when clamping an article which is grasped between the jaws. A clamping and/or spreading tool of this kind has proved very successful in everyday use.
U.S. Pat. No. 6,568,667 discloses a clamping and/or spreading tool comprising an identical stepping gear transmission and an additional quick-lock drive which operates to close the clamping jaws, i.e. to shift the movable jaw towards the stationary jaw when a draw-back lock preventing displacement of the push or pull rod contrary to the advance direction of the stepping gear transmission is actuated. The prime mover of the quick-lock drive is embodied by a helical compression spring acting between points of attachment at a side of the support remote from the movable jaw. It is a disadvantage of this quick-lock mechanism that much space is required to offer the quick-lock mechanism the path needed for unfolding the driving power stored. As the compression spring assembly needs a long drive path for the driving power to unfold, clamping and/or spreading tools of this kind have not only a great axial extension but also great weight, making such tools unwieldy to handle. Moreover, nonlinear power output accompanies the helical compression spring, in other words great thrust occurs at the beginning of the closing motion, diminishing gradually in the course of the closing motion. Above all, the known drive bears a risk of injury since the movable jaw closes explosively.